1. Field of the Invention
The present disclosure relates to a nickel-based super heat resistant alloy and a method of manufacturing the same.
2. Description of the Related Art
Parts such as an engine and a gas turbine used in thermoelectric power plants or aircrafts are made of a nickel-based superalloy.
However, a crack or damage may occur due to use over a long period of time at high temperatures, and thus threat stability of the thermoelectric power plants and the aircrafts. Accordingly, research on a nickel-based superalloy having an improved creep property has been conducted.
Meanwhile, since a very high temperature reactor has high efficiency and economic feasibility as the very high temperature reactor is operated at high temperatures, research on embodiment of a very high temperature gas reactor by increasing an output temperature of a nuclear reactor to 950° C. to increase efficiency and further produce clean hydrogen using heat thereof has been actively conducted. Therefore, soundness of materials constituting the very high temperature reactor need to be maintained at very high temperatures.
Inactive helium gas having excellent thermal conductivity and absorbing neutrons in a small amount is used as a coolant of the very high temperature gas reactor, and heat exchanger parts for heat exchanging of a primary coolant and a secondary coolant are exposed to the most severe environment.
Currently, examples of a material considered as a material of a heat exchanger of the very high temperature reactor broadly include Alloy 617, Hastelloy XR, and Alloy 230. All of the examples is the nickel-based superalloy including nickel as a main element, among three types of materials, the most important Alloy 617 having an excellent mechanical property at high temperatures is actively evaluated in the US and France. In France, research on Alloy 230 as well as Alloy 617 has been conducted, and in Japan, research on Hastelloy XR has been mainly conducted.
According to current documents, there is no large difference in creep behavior at high temperatures of 900° C. or more for Alloy 617, Hastelloy XR, and Alloy 230. However, it is known that Alloy 230 is weak to carburizing when Alloy 230 is tested over a long period of time in a helium environment, and a deterioration speed of the material is fast in a very high temperature environment of 950° C. to serve as a limitation factor in maintenance of stability over a long period of time, and thus a solving method thereof is required.
It is known that helium considered as the coolant in the very high temperature reactor has an inactive property and may include an impurity in a small amount. However, the impurity included in helium serves as a factor causing corrosion of a surface of the very high temperature reactor in the very high temperature environment. Moisture and a hydrogen component are materials always included in helium due to system leakage and outgassing, and are reacted with carbon in the nuclear reactor to generate carbon monoxide and methane. Carbon monoxide and methane thusly produced may cause corrosion at high temperatures. Further, there may occur problems in that brittleness is increased during carburizing, and on the contrary, creep resistance is reduced during decarburizing.
Meanwhile, the alloys are not materials developed for the very high temperature gas reactor, but provided to be used in a wide high temperature range (600 to 850° C.). The superalloys improve temperature resistance at about 700 to 800° C. because a γ′ (gamma prime) phase is present.
However, since the gamma prime phase is not stable at 950° C. that is a target temperature of the very high temperature environment, mechanical soundness cannot be secured at very high temperatures by the same method. Further, deterioration of the material is accelerated due to continuous corrosion. In order to perform a role as a structural material, high temperature creep resistance as well as a tensile property at normal temperature and high temperatures needs to be excellent.
As an existing technology relating to the nickel-based super heat resistant alloy, Korean Patent No. 10-0203379 discloses a nickel-based super heat resistant alloy for casting. Specifically, there is disclosed a nickel-based super heat resistant alloy for casting, including Ni as a basic composition and 6 to 10% of Cr, 8 to 13% of W, 1 to 4% of Mo, 3 to 7% of Al, 0.5 to 3% of Ti, 0.5 to 3% of Nb, 8 to 12% of Co, 3 to 7% of Ta, 0.05 to 2.0% of Hf, 0.05 to 2.0% of Zr, 0.01 to 0.1% of B, and 0.01 to 0.5% of C.
Accordingly, the present inventors have conducted a study of a method of improving a creep property and a corrosion property of the nickel-based super heat resistant alloy at high temperatures, and found that an amount of solid solution strengthening elements (Cr, Co, Mo, W, or Ta) is controlled and Al is included to improve the creep property and the corrosion property, thereby accomplishing the present invention.